Re: [Qemu-devel] [PATCH] oslib-posix: Use MAP_STACK in qemu_alloc_stack() on OpenBSD

[Kamil Rytarowski]

On 11.10.2018 11:36, Peter Maydell wrote:
> On 11 October 2018 at 00:55, Brad Smith <address@hidden> wrote:
>> And from FreeBSD...
>>
>>      MAP_STACK MAP_STACK implies MAP_ANON, and offset of 0.  The fd
>> argument must be -1 and prot must include at least
>> PROT_READ and PROT_WRITE.
>>
>> This option creates a memory region that grows to at
>> most len bytes in size, starting from the stack top
>> and growing down.  The stack top is the starting
>> address returned by the call, plus len bytes.  The
>> bottom of the stack at maximum growth is the starting
>> address returned by the call.
>>
>> Stacks created with MAP_STACK automatically grow.
>> Guards prevent inadvertent use of the regions into
>> which those stacks can grow without requiring mapping
>> the whole stack in advance.
> 
> Hmm. That "automatically growing" part sounds like
> behaviour we definitely do not want for our use case.
> So we're going to need to make this OS-specific :-(
> 

I propose to restrict MAP_STACK it to OpenBSD (with a comment in the
code). Once it will be needed by someone else will be able to enable it
for other OSes.

> thanks
> -- PMM
>

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